The present invention relates generally to devices for cutting sound grooves in a disc recording medium. More particularly, the device has excellent recording characteristics since signals are recorded by a cutting stylus, while continuous chips, cut from the original record discs, are prevented from adhering to the groove, the cutting stylus, and other parts, by effectively lessening generation of the static electricity and discharging the static electricity thus generated during the cutting process.
Sound signals are ordinarily recorded on an original record disc coated with a nitrocellulose and alkyd resin base material, that is, a so-called "lacquer disc". Recording involves cutting a groove thereon by means of a device having a cutting stylus. As a material for this cutting stylus, sapphire has heretofore been used. However, a sapphire has a short serviceable life (life time of the order of ten or twenty times of cutting the surface of the original record disc) because it is not very hard and has a relatively rapid wear.
Accordingly, attempts have been made to use a harder diamond, in place of a sapphire, for the cutting stylus. The life of a diamond cutting stylus is undoubtedly very long, because of the hardness of diamond. However, it has been found that a diamond stylus generates more static electricity during recording than a sapphire generates, since diamond is a carbonaceous material. For a diamond stylus, different kinds of electrostatic charges accumulate on the confronting surfaces of the continuous chip and the cutting stylus and on the confronting surfaces of the chip and the groove after cutting. When such a great quantity of static electricity is generated, the resulting coulomb force causes the chip to adhere to the cutting stylus and the cut groove of the lacquer disc. It is difficult to remove this chip, even by means of a vacuum suction, which has been used heretofore.
When the chip adheres to the cutting stylus and the lacquer disc, the cutting function is impaired. For this reason, cutting styluses employing diamond tips have not been used heretofore.
Accordingly, in order to overcome the above described difficulties, we have previously proposed and practiced a cutting device having a grounded electroconductive material thin plate on the mirror surface of a diamond stylus. In accordance with this previous cutting device, the chip produced at the time of cutting is guided into contact with the electroconductive material thin plate. The electrostatic charge accumulated on the chip escapes to ground by way of the electroconductive material thin plate, thereby preventing static electricity.
However, after this cutting stylus has been used a great number of times, the electroconductive material thin plate becomes worn by abrasion and/or it peels off from the diamond cutting stylus structure. This gives rise to the drawback of short serviceable life.
Accordingly, with the aim of further over coming the problems of the above mentioned, previously proposed device, we have previously proposed and practiced a device for cutting sound grooves in disc recording mediums as disclosed in U.S. Pat. No. 4,105,213. This device is organized, based on the consideration on the principle by which static electricity is generated when two objects of different compositions come into mutual contact and then separate. The device uses a structure made of a substance, such as a corundum, which does not readily generate static electricity. This substance is adhered to the mirror surface of the diamond stylus proper. The chip cut from the original record disc comes into contact with and is guided by this structure, which does not readily generate static electricity. According to this device, although diamond is used for the cutting stylus structure, static electricity is not easily generated, whereby the problem of adhering of the cutting chip to parts such as the cutting stylus does not readily occur, and greatly improved results were achieved.
However, even in this device, since a substance which does not readily generate static electricity is caused to adhere to the diamond cutting stylus structure, this substance peels and falls off from the cutting stylus structure after the cutting stylus has been used a great number of times. Particularly in the device of a construction wherein a recess is provided at the tip part of the mirror surface of the cutting stylus structure, and a small piece of sapphire is embedded in this recess, the separation of the sapphire from the cutting stylus structure does not readily occur, but, on the other hand, the fabrication is difficult and gives rise to high cost. Furthermore, as the tip of the cutting stylus becomes worn through abrasion, the tip part is chipped, and the small piece of sapphire also drops off. As a net result, the serviceable life of the cutting stylus is not very long. The serviceable life of this device has been found to be of an order such that it can withstand the cutting of from 50 to 100 faces of original record discs.
Accordingly, the present invention comtemplates the provision of a record groove cutting device of a novel organization by which the generation of static electricity is suppressed, and, at the same time, any static electricity which is generated is discharged to ground (earth) without attaching a small piece, thin plate, or the like of a substance different from the diamond cutting stylus structure to the cutting stylus structure as in the above described two devices previously proposed and practised.
Accordingly, it is a general object of the present invention to provide a novel and useful device for cutting a sound groove on a disc recording medium, in which the above described problems have been solved.
Another and specific object of the invention is to provide a device for cutting a sound groove in a disc recording medium which device has a cutting stylus of a construction wherein at least the mirror surface of the diamond cutting stylus structure has been subjected to an ion implantation process, and the mirror surface has been rendered electroconductive. In the device of the invention, since the mirror surface of the cutting stylus has been made conductive, there is little generation of static electricity even when the cut chip rubs against the mirror surface. Furthermore, since any electrostatic charge which is generated is permitted to escape toward ground, the adhering of the chip due to static electricity to the cutting stylus, the cut groove of the original disc, and other parts is prevented. Still another advantageous feature of this device is that, since ions have been implanted to a specific depth in the surface portion of the cutting stylus structure, there are no undesirable occurrences such as peeling, dropping off, or disappearance of a thin plate or small piece of an electroconductive material, a substance which does not readily generate static electricity, and the like from the cutting stylus as in the aforedescribed proposed device.
Other objects and further features of the invention will be apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings.